From 0b213c9090369ff43060816aed38cb6c67e228f8 Mon Sep 17 00:00:00 2001
From: Maksim Panchenko <maks@fb.com>
Date: Mon, 3 Oct 2022 18:50:18 -0700
Subject: [PATCH] [BOLT] Fix writing out unmarked .eh_frame section

When BOLT updates .eh_frame section, it concatenates newly-generated
contents (from CFI directives) with the original .eh_frame that has
relocations applied to it. However, if no new content is generated,
the original .eh_frame has to be left intact. In that case, BOLT was
still writing out the relocatable copy of the original .eh_frame section
to the new segment, even though this copy was never used and was not
even marked in the section header table.

Detect the scenario above and skip allocating extra space for .eh_frame.

Reviewed By: rafauler

Differential Revision: https://reviews.llvm.org/D135223
---
 bolt/lib/Rewrite/RewriteInstance.cpp | 10 ++++++++++
 bolt/test/X86/dummy-eh-frame-bug.s   | 27 +++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100644 bolt/test/X86/dummy-eh-frame-bug.s

diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index 16e2db8269eeb..53ce8d1d68538 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -3798,6 +3798,16 @@ void RewriteInstance::mapDataSections(RuntimeDyld &RTDyld) {
   if (RuntimeLibrary *RtLibrary = BC->getRuntimeLibrary())
     RtLibrary->addRuntimeLibSections(Sections);
 
+  if (!EHFrameSection || !EHFrameSection->isFinalized()) {
+    ErrorOr<BinarySection &> OldEHFrameSection =
+        BC->getUniqueSectionByName(Twine(getOrgSecPrefix(), ".eh_frame").str());
+    if (OldEHFrameSection) {
+      RTDyld.reassignSectionAddress(OldEHFrameSection->getSectionID(),
+                                    NextAvailableAddress);
+      BC->deregisterSection(*OldEHFrameSection);
+    }
+  }
+
   for (std::string &SectionName : Sections) {
     ErrorOr<BinarySection &> Section = BC->getUniqueSectionByName(SectionName);
     if (!Section || !Section->isAllocatable() || !Section->isFinalized())
diff --git a/bolt/test/X86/dummy-eh-frame-bug.s b/bolt/test/X86/dummy-eh-frame-bug.s
new file mode 100644
index 0000000000000..2d05cf3d88d78
--- /dev/null
+++ b/bolt/test/X86/dummy-eh-frame-bug.s
@@ -0,0 +1,27 @@
+# REQUIRES: system-linux
+
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-linux %s -o %t.o
+# RUN: ld.lld %t.o -o %t.exe -q
+# RUN: llvm-bolt %t.exe -o %t.bolt.exe --funcs=nocfi_function
+# RUN: llvm-readelf --section-headers %t.bolt.exe | FileCheck %s
+
+## Check that llvm-bolt does not allocate unmarked space for original .eh_frame
+## after .text when no update is needed to .eh_frame.
+
+# CHECK: {{ .text}} PROGBITS [[#%x,ADDR:]] [[#%x,OFFSET:]] [[#%x,SIZE:]]
+# CHECK-NEXT: 0000000000000000 [[#%x, OFFSET + SIZE]]
+
+  .text
+  .globl nocfi_function
+  .type nocfi_function,@function
+nocfi_function:
+  ret
+  .size nocfi_function, .-nocfi_function
+
+  .globl _start
+  .type _start,@function
+_start:
+  .cfi_startproc
+  call nocfi_function
+  .size _start, .-_start
+  .cfi_endproc